1. Field of the Invention
The present invention relates to a novel Ni—Fe based super alloy and a process of producing the super alloy. Also, the present invention relates to a turbine disk using the super alloy, a process of producing the turbine disk, a turbine spacer using the super alloy, and a process of producing the turbine spacer, as well as to a gas turbine.
2. Description of the Related Art
Increasing combustion temperature is effective to increase the efficiency of power generation in a gas turbine power plant. A rotor as a rotating component of the gas turbine comprises a turbine stub shaft and a plurality of turbine disks coupled to the turbine stub shaft by turbine stacking bolts with turbine spacers each interposed between adjacent turbine disks.
The rotor is not directly exposed to combustion gases and is cooled by using a part of compressed air used for combustion. Therefore, temperatures of the above-mentioned rotor components are fairly lower than those of turbine (rotating) blades and turbine (stator) nozzles which are directly exposed to the combustion gases. Therefore, 12Cr steel disclosed in Patent Document 1; JP,A 63-171856 has been used in the turbine rotor so far. With a recent increase of the combustion temperature and the compression rate, however, Ni—Fe based super alloys containing Fe and having superior high-temperature strength, such as IN718 and IN706, have become more commonly used. In those alloys, the γ″ phase (Ni3Nb) is finely precipitated with addition of Nb, whereby a superior strength characteristic is obtained. Also, those alloys have superior productivity in making a large-sized ingot in spite of being the Ni based super alloys.
Patent Document 2; JP,A 10-226837 discloses, as an improved material of IN706, a Ni—Fe based super alloy containing not less than 0.05% by weight of C+N, 10-20% of Cr, 25-45% of Fe, 0.5-2.0% of Al, 1.0-2.0% of Ti, and 1.5-3.0% of Nb.
Further, Non-Patent Document 1; CAMP-ISIJ, VOL. 15 (2003)—535p, states that regarding an alloy containing 0.3-1.5% of Al and 1.8-3.0% of Nb as an improved material of IN706, the γ″ phase is not observed and only the γ′ phase is observed.